Pipe guides and methods of guiding pipes in snubbing units

ABSTRACT

An hydraulic snubbing unit has a pair of hydraulic cylinders for moving travelling snubbing slips towards and away from stationary snubbing slips to snub a pipe through the snubbing unit, the hydraulic cylinders having spaced, parallel cylinder rods. A pipe guidance apparatus has pipe guides between the stationary snubbing slips and the travelling snubbing slips, the pipe guides each having a pair of cylinder rod openings spaced apart from one another and slidably receiving the rods of the hydraulic cylinders and a pipe guidance opening located between the cylinder rod openings and slidably guiding the pipe, and a pipe guide spacer having extendable and contractible interconnections between the pipe guides. In a contracted condition of the pipe guide spacer, the interconnections are contracted and the pipe guides are moved into proximity to one another by the simultaneous movement of the cylinder rods slips towards the stationary slips, and in an expanded condition, the interconnections are extended and the pipe guides are moved apart from one another by the simultaneous movement of the cylinder rods away from the stationary slips to provide lateral support of the pipe at intervals along the pipe.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to pipe guides for use in snubbing unitsfor snubbing pipes into and from live underground well bores, tosnubbing units provided with pipe guides and to methods of guiding pipesthrough snubbing units.

2. Description of the Related Art

Snubbing units, which are used to “snub” or feed pipes into and fromunderground wells, employ stationary snubbing slips or grippers andtraveling snubbing slips to alternately grip and release a pipe as thetraveling snubbing slips are moved towards and away from the stationarysnubbing skips, so that the pipe is moved upwardly or downwardly by a“hand-over-hand” gripping of the pipe.

Traditional pipe guidance apparatus on snubbing units used todaytypically employ two interlocking and telescoping tubes positionedbetween the stationary snubbing slips and the traveling snubbing slips.Inherent problems with this type of guiding system include the space andweight of the pipe guidance systems and the heights which they add tothe snubbing units. Also, approximately one half of the effective strokeof the snubbing unit is lost and snubbing operations therefore becomemuch less efficient than would be the case if full snubbing strokescould be taken.

A pipe that is being snubbed into or out of a live well against theforces (compressive loads), which are generated from the well pressureover the cross-sectional area of the pipe being removed from or insertedinto the well bore, can only support a limited amount of compressiveforce before the pipe buckles. The longer the length of exposed pipebetween the point at which the traveling snubbing slips grip the pipeand the point at which the pipe is exposed outside of the well boredetermines the allowable compressive load before buckling takes place.For example a 2-foot long section (window) of exposed and unsupportedpipe under a compressive load can withstand a far greater compressiveforce, before major axis buckling occurs, than a 10-foot unsupportedsection subject to the same compressive load.

There are two types of bucking that can occur when a pipe is under acompressive load:—

-   -   1. Major Axis buckling occurs without of yielding the pipe and        is therefore known as elastic buckling. This happens when        compressive loads on the pipe are as such that the pipe buckles        outwardly, at an exposed, i.e. laterally unsupported, section of        the pipe as a result of not being supported laterally.    -   2. Local buckling requires the pipe to yield and is therefore        known as inelastic buckling. This happens when the pipe may very        well be supported laterally but the compressive load is as such        that the pipe is effectively crushed vertically.

When snubbing against well pressures without pipe guidance apparatus, areasonable safety factor to prevent buckling can be obtained by notexposing a section of pipe longer than the pipe can support from thegenerated forces with friction related to the seal point maintaining thewell pressure. Additional factors, such as the speed at which the pipeis inserted into or removed from the well, are all part of typicalpre-job calculations which are needed to predetermine the maximumallowable length of pipe that can be exposed while manipulating the pipewithout possible bucking. Once these calculations have been made, asnubbing operator uses short strokes to move the pipe into or out of thewell, never allowing more unsupported exposure than calculated.

With this type of snubbing operation, a safety factor is only maintainedif the snubbing operator stays within the calculated parameters. Theoperation is therefore subject to human error in the event that theoperator uses too long a stroke of the pipe, which could result in thepipe rocketing out sideways at an exposed, i.e. laterally unsupported,section of the pipe. This type of error, although not common, can easilyoccur, since operators are under constant pressure to complete snubbingoperations as quickly as possible and they therefore generally push thelimits by attempting to take strokes which are as big as possible.Often, an operator will take a stroke long enough to see the pipe bow asit is being snubbed into or out of the well. This bowing occurs justshort of the pipe reaching its compression limit. The result of buckingof the pipe can be catastrophic, with potential loss of control of thepipe and the well and loss of life. The short-stroking operation is notonly dangerous but slows the operation down as compared to longerstrokes of exposed pipe that could be taken if the pipe was supportedexternally by means of a pipe guidance apparatus.

Hydraulic snubbing units generally comes in two configurations, namely aself-contained, stand-alone configuration, and a rig-assist snubbingunit.

The self contained stand-alone configuration works well for live wells,where the overall height of the equipment is not all that importantbecause there is typically no spatial limitations in order to handle thepipe that is to be inserted or removed from the live well.

With a rig assist-snubbing unit, however, the overall height is criticalbecause the snubbing unit must work within the height restraint of thetop of a derrick forming part of a rig in conjunction with which thesnubbing unit is being operated. The distance between the top of thesnubbing unit and the inside working area from the top of the rigderrick in many cases eliminates the option of having pipe guidanceapparatus, because the additional height that the apparatus would add tothe snubbing unit would not allow sufficient space for lengths of pipeto be handled. Consequently, the operators have resorted to performingthe dangerous short stroking operation on high-pressure wells, asdescribed above.

BRIEF SUMMARY OF THE INVENTION

According to the present invention, there is provided a pipe guidanceapparatus for guiding a pipe during snubbing of the pipe, the pipe guidehaving a plurality of pipe guides, each with a pair of jack rod openingsspaced apart from one for sliding engagement with a pair of parallel,spaced hydraulic jack rods, which laterlly restrain the pipe guides whenthe apparatus is in use, and a pipe guidance opening located between thejack rod openings for slidable guiding engagement with the pipe. Thejack rod openings are mutually aligned and the pipe guidance openingsare also mutually aligned. The pipe guidance apparatus includes a pipeguide spacer comprising extendable and contractible interconnectionsbetween the pipe guides. The pipe spacer has a contracted condition, inwhich the interconnections are contracted and the pipe guides are movedtowards one another, and an expanded condition, in which theinterconnections are extended and the pipe guides are moved apart fromone another.

In a preferred embodiment of the present invention, the extendable andcontractible interconnections comprise two parallel sets of tubularmembers, the tubular members of each of the sets being telescopicallyextensible and retractable relative to one another and each of the setsof tubular members being provided at one end of the set with aconnecting member, e.g. a rod, for telescopically extending the tubularmembers.

Also in accordance with the present invention, there is provided anhydraulic snubbing unit having stationary snubbing slips, travelingsnubbing slips and a pair of spaced, parallel hydraulic jacks for movingthe traveling snubbing slips towards and away from the stationarysnubbing slips to snub a pipe through the snubbing unit, the hydraulicjacks comprising cylinders having jack rods. The hydraulic snubbing unitis provided with a pipe guidance apparatus for guiding a section of thepipe between the stationary snubbing slips and the travelling snubbingslips, and the pipe guidance apparatus comprises a plurality of pipeguides between the stationary snubbing slips and the travelling snubbingslips, the pipe guide guides each having a pair of jack rod openingsspaced apart from one another and slidably receiving the jack rods, anda pipe guidance opening located between the cylinder rod openings andslidably guiding the pipe. The pipe guidance apparatus includes a pipeguide spacer comprising extendable and contractible interconnectionsbetween the pipe guides, the pipe spacer having a contracted condition,in which the interconnections are contracted and the pipe guides aremoved into proximity to one another by the movement of the travelingslips towards the stationary slips, and an expanded condition, in whichthe interconnections are extended and the pipe guides are moved apartfrom one another by the movement of the traveling slips away from thestationary slips.

In the preferred embodiment of the invention, the extendable andcontractible interconnections comprise two parallel sets of tubularmembers, the tubular members of each of the sets being telescopicallyextensible and retractable relative to one another, and each including aconnecting member for telescopically extending and contracting thetubular members, the connecting members each having one end connectedfor movement with the traveling slips and an opposite end extending intothe tubular members.

Also according to the present invention, there is provided a method ofguiding a pipe as the pipe is being snubbed through snubbing unit havingstationary snubbing slips, traveling snubbing slips and spaced, parallelhydraulic jacks for moving the traveling slips towards and away from thestationary slips, the hydraulic jacks comprising hydraulic cylindershaving jack rods connected to the traveling snubbing slips, the methodcomprising the steps of gripping the pipe by the traveling snubbingslips during movement of the pipe through the snubbing unit, extendingand retracting the hydraulic cylinders to displace the travelingsnubbing slips relative to the stationary snubbing slips and thereby todisplace the pipe through the snubbing unit, and guiding a section ofthe pipe extending between the stationary snubbing slips and thetravelling snubbing slips by laterally restraining the pipe section atintervals spaced apart along the section of the pipe.

Prefereably, the pipe is guided by pipe guides spaced apart along thesection of the pipe, and the pipe guides are moved towards one anotheron movement of the travelling slips towards the stationary slips andapart from one another on movement of the travelling slips away from thestationary slips by sliding engagement of the pipe guides with the jackrods of the hydraulic cylinders.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be more readily understood from the followingdescription of an embodiment thereof given, by way of example only, withreference to the accompanying drawings, in which:—

FIG. 1 shows a view in elevation of a pipe snubbing unit provided withan extendable and contractible pipe guidance apparatus according to thepresent invention, with the pipe guidance apparatus in a contractedcondition;

FIG. 2 shows a view corresponding to that of FIG. 1 but with the pipeguidance apparatus in an extended condition;

FIG. 3 shows a plan view of a pipe guide forming part of the pipeguidance apparatus of FIGS. 1 and 2;

FIG. 4 shows a view in side elevation of the pipe guide of FIG. 3;

FIGS. 5 and 6 show views in vertical cross-section through a set oftubular members forming part of the pipe guidance apparatus of FIGS. 1and 2 in a contracted condition and an extended condition, respectively:and

FIG. 7 shows a broken-away view in perspective of a connection betweenone of the tubular members of FIGS. 5 and 6 and an associated guideplate.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring firstly to FIGS. 1 and 2 of the accompanying drawings, thereis shown a pipe snubbing unit, indicated generally by reference numeral10, for snubbing a vertical pipe 12 into or from an underground well(not shown).

The snubbing unit 10 has stationary snubbing slips or pipe grippers 14,provided with an underlying blow-out preventor 16, travelling snubbingslips or pipe grippers 18 and a pair of hydraulic jacks 20 for movingthe travelling snubbing slips 18 vertically towards and away from thestationary snubbing slips 14.

The jacks 20 each comprise an hydraulic cylinder 22 from which extendsan jack rod 24, the lowermost end of the hydraulic cylinder 22 beingmounted on a middle plate 26, and the uppermost end of the jack rod 24being connected to a travelling plate 28 on which the travellingsnubbing slips 18 are mounted.

In operation of the snubbing unit 10, the jack rods 24 move thetravelling snubbing slips 18 vertically up and down relative to thestationary snubbing slips 14, while the stationary snubbing slips 14 andthe travelling snubbing slips 18 alternately grip the pipe 12. In thisway, the pipe 12 is fed into or from its well by the snubbing slips 14and 18 by a “hand-over-hand” operation of those slips.

The snubbing unit 10, as described above, and its operation are wellknown in the art and, therefore, are not described herein in greaterdetail.

To provide lateral support for a section 30 of the pipe 12 extendingbetween the stationary snubbing slips 14 and the traveling snubbingslips 18 when the traveling snubbing slips 18 are displaced by thehydraulic jack rods 24 from the stationary snubbing slips 14, thesnubbing unit 10 is equipped with a pipe guidance apparatus indicatedgenerally be reference numeral 32 in FIG. 1, the components of which areshown in greater detail in FIGS. 3-7.

The pipe guidance apparatus 32 includes four pipe guides 34, one ofwhich is shown in FIGS. 2 and 3.

Each pipe guide 34 includes an elongate guide plate which, as can beseen from FIG. 4, has a pair of parallel flat end portions 38, a centralportion 40 which is parallel to the flat end portions 38, and a pair ofintermediate portions 42 which extend between and at an inclination tothe end portions 36 and the central portion 38. Each intermediateportion 42 is provided, in one of its edges, with a pair of threadedholes 45.

Each of the end portions 38 is formed with a circular jack rod opening44, and each circular jack rod opening 44 is provided, at opposite sidesof its respective end portion 38, with an annular slide member 46, whichis secured to the end portion 38 by screws 48.

The circular jack rod openings 44 slidably receive the jack rods 24, asshown in FIGS. 1 and 2, so that the pipe guides 34 are guided andretained laterally of the jack rods 24 by slidable engagement with thejack rods 24 and are free to slide longitudinally of the jack rods 24.The jack rods 24 hold the pairs of jack rod openings 44 in mutualalignment and thereby also hold pipe openings 50 in mutual alignment.

The pipe openings 50, which are provided with annular slide members 52secured to the central portion 40 by screws 54, slidably receive, guideand laterally restrain the pipe section 30, extending between thestationary snubbing slips 14 and the traveling snubbing slips 18, sothat the pipe section 30 is prevented from buckling.

Referring now to FIGS. 2, 5 and 6, the pipe guides 34 are connected toone another by pipe spacers indicted generally by reference numeral 55in FIG. 2. The pipe spacer 55 includes two sets of interconnectionswhich are formed by two sets of telescopically extensible andretractable tubular members 54 a-54 d, as shown in greater detail inFIGS. 5 and 6. The pipe guidance apparatus therefore has a collapsibleladder-like assembly, formed by the rung-like pipe guides 34 and thestile-like sets of tubular members 54 a-54 d.

The pipe spacer 55 has a contracted condition, in which theinterconnections comprising the sets of tubular members 54 arecontracted and the pipe guides 34 are moved into proximity to oneanother by the movement of the traveling snubbing slips 18 towards thestationary snubbing slips 14 as shown in FIG. 1, and an expandedcondition, in which the sets of tubular members 54 are telescopicallyextended relative to one other and the pipe guides 34 are moved apartfrom one another, as the traveling snubbing slips are moved away fromthe stationary snubbing slips 14 by the hydraulic jacks rods 24, asshown in FIG. 2. In the expanded condition of the pipe spacer 55, inwhich the pipe guides 34 are spaced apart along the pipe section 30,longitudinally of the pipe 12, for laterally supporting the pipe section30 at these spaced apart positions as shown in FIG. 2.

The two sets of tubular members 54 a-54 d are each provided with aconnecting member in the form of a rod 56 for telescopically extendingand contracting the tubular members 54 a-d. Each of the rods 56 has anupper end 58 connected to the traveling plate 28, and thereby connectedfor movement vertically with the traveling snubbing slips 18, and alower end 60 extending into the innermost tubular member 54 a. When thetraveling snubbing slips 18 are displaced upwardly, away from thestationary slips 14 by extension of the jack rods 24 from theircylinders 22, the rods 56 pull the associated tubular members 54 a-54 dso as to telescopically extend the latter.

As shown in FIGS. 5 and 6, the lower end 60 of the rod 56 has an a metalannular anchor member 62 a, which is secured to the lower end 60 by anut 64 in threaded engagement with the lower end 60. The anchor member62 a includes an annular rubber cushion 66, which is provided on thelower end 60 at the side of the anchor member 62 opposite from the nut64.

The tubular members 54 a-54 d have caps 68 a-68 d in threaded engagementwith the upper ends of the respective tubular member 54 a-54 b. Each ofthe caps 68 b-68 d is formed with a circular opening 70 b-70 d forslidably receiving a respective one of the tubular members 54 b-54 d,while the cap 68 a of the innermost tubular member 54 a has a circularopening 70 a for slidably receiving the rod 56. Each of the tubularmembers 54 a-54 c has an annular anchor member 62 a-62 c, welded to itsexterior at a spacing from its lower end, the annular anchor members 62a-62 c being provided with annular cushions 62 a-62 c of resilientmaterial, e.g. rubber.

Since the caps 68 a-68 d are secured by threaded engagement with thetubular members 54 a-54 d, the caps 68 a-68 d can be readily unscrewedand removed from the tubular members 54 a-54 d to allow replacement ofthe annular cushions 62 and 62 a-62 c and for other maintenance andrepairs.

The caps 68 a-68 d serve as end abutments on the tubular members 54 a-54d, so that when the rod 56 is drawn upwardly relative to the innermosttubular member 54 a, by upward displacement of the traveling snubbingslips 18 as described above, the rubber cushion 66 of the anchor member62 is moved into abutment with the end cap 68 a, which causes theinnermost tubular member 54 a to be telescopically extended from thenext tubular member 54 b.

The cushion 66 b of the tubular member 54 b is then moved upwardly intoabutment with the end cap 68 a, which causes the tubular member 54 b tobe telescopically extended from the tubular member 54 c. The tubularmember 54 c is then telescopically extended in a similar manner from theoutermost tubular member 54 d, thereby extending the pipe guide spacer55 into the extended condition shown in FIG. 2.

The lower end of the tubular member 54 d is closed by a circular plate72, which is welded to the lower end of the tubular member 54 d. Whenthe traveling snubbing slips 18 reverse their direction of movement andmove towards the stationary snubbing slips 14, the rod 12 acts as a pushrod and is telescopically retracted into the innermost tubular member 54a. The tubular members 54 a-54 c are then telescopically retracted intothe outermost tubular member 54 d until the lower ends of the tubularmembers 54 a-54 c abut the circular plate 72, as shown in FIG. 6.

FIG. 7 shows a connection between one of the guide plates 34 and itsassociated tubular member 54 a. This connection is provided by a metalstrip 76, which is secured, by screws 77 in threaded engagement with theholes 45 (FIG. 4), to an edge of one of the inclined portions 42 of theguide plate 34. The metal strip 76 is connected to the cap 68 a by ametal plate 78, which is welded to the metal strip 76 and to the cap 68a.

The remaining tubular members 54 b-54 d are connected to their guideplates 34 by connections which are similar to that shown in FIG. 7, andwhich have metal plates which correspond to the metal plate 78 of FIG. 7but which are of different dimensions to accommodate the differentdiameters of the tubular members 54 a-54 d.

When the above-described pipe guidance apparatus 32 is in use, thesection 30 of the pipe 12 which is exposed between the stationarysnubbing slips 14 and the traveling snubbing slips 18 is automaticallyguided and laterally restrained by the mutually spaced pipe guides 34when the traveling snubbing slips 18 are moved away from the stationarysnubbing slips 14 by the hydraulic jack rods 24, which causes the pipespacer 55 to become extended without any intervention by an operator.Therefore, the maximum allowable stroke by which the pipe 12 is snubbedcan be employed but no judgement with respect to the length of strokenor any other intervention by an operator is required to preventbuckling of the pipe section 30. Human error in determining the strokelength is therefore avoided and, consequently, highly efficient snubbingof the pipe 12 without buckling of the pipe 12 can be achieved. Also,the height of the snubbing unit 10 is not affected by the provision ofthe snubbing unit 10 with the pipe guidance apparatus 32.

The anchor members 62 a-62 c are staggered along their tubular members54 a-54 c, as shown in FIGS. 5 and 6, to compensate for the heights ofthe caps 68 a-68 c, so that the tubular members 54 a-54 c are extendedby equal lengths when the pipe spacer 55 is in its extended condition.

The pipe guides 34 shown in the drawings are each formed with adepressed central portion 40 to conform to the shapes of the slipsbetween the stationary snubbing slips 14 and the travelling snubbingslips 18 when the snubbing unit is collapsed and thereby to avoid addingadditional height to the snubbing unit. Otherwise, the pipe guidescould, for example, be flat.

The tubular members are provided, at their lower ends, with annularmetal rings 74 a-74 d, which are welded to the exteriors of the tubularmembers 54 a-54 d and which serve to provide internal stabilization ofthe apparatus.

As will be apparent to those skilled in the art, various modificationsmay be made in the above-described embodiment of the present inventionwithin the scope of the appended claims.

1. A pipe guidance apparatus for guiding a pipe during snubbing of the pipe, comprising:— a. a plurality of pipe guides; b. the pipe guides each having a pair of jack rod openings spaced apart from one and a pipe guidance opening located between the jack rod openings for slidably guiding the pipe; c. the jack rod openings being mutually aligned and the pipe guidance openings being mutually aligned; and d. a pipe guide spacer; e. the pipe guide spacer comprising extendable and contractible interconnections between the pipe guides; and f. the pipe spacer having a contracted condition, in which the interconnections are contracted and the pipe guides are moved towards one another, and an expanded condition, in which the interconnections are extended and the pipe guides are moved apart from one another.
 2. A pipe guidance apparatus as claimed in claim 1, wherein the extendable and contractible interconnections comprise two parallel sets of tubular members, the tubular members of each of the sets being telescopically extendable and retractable relative to one another and each of the sets of tubular members being provided, at one end of the set, with a pull member for telescopically extending the tubular members.
 3. A pipe guidance apparatus as claimed in claim 2, wherein an outermost one of the tubular members of each set of tubular members, at an opposite end of the set, has an abutment for retaining the remainder of the set on contraction of the set.
 4. A pipe guidance apparatus as claimed in claim 2, wherein each of the pull members has, at one end thereof, an anchor member located within an innermost one of the tubular members of the respective set of tubular members, said innermost tubular member having an end abutment engageable by the anchor member to telescopically extend said respective set of tubular members on extension of the pull member from the innermost tubular member.
 5. A pipe guidance apparatus as claimed in claim 4, wherein each of the tubular members has, on one end thereof, a further anchor member and at an opposite end thereof a further end abutment, the further end abutment of each of the tubular members being engageable by the further anchor member of another of the tubular members to effect the telescopic extension of the tubular members.
 6. A pipe guidance apparatus as claimed in claim 5, wherein the further end abutments are formed by end caps on the tubular members.
 7. A pipe guidance apparatus as claimed in claim 5, wherein the further anchor members comprise annular collars on the tubular members.
 8. In an hydraulic snubbing unit having stationary snubbing slips, travelling snubbing slips and a pair of spaced, parallel hydraulic jacks for moving the travelling snubbing slips towards and away from the stationary snubbing slips to snub a pipe through the snubbing unit, the hydraulic jacks comprising hydraulic cylinders and jack rods extending from the cylinders, the improvement comprising: a pipe guidance apparatus for guiding a section of the pipe between the stationary snubbing slips and the travelling snubbing slips; the pipe guidance apparatus comprising:—a plurality of pipe guides between the stationary snubbing slips and the travelling snubbing slips; the pipe guide guides each having a pair of cylinder rod openings spaced apart from one another and slidably receiving the jack rods of the hydraulic cylinders and a pipe guidance opening located between the cylinder rod openings and slidably guiding the pipe; and a pipe guide spacer; the pipe guide spacer comprising extendable and contractible interconnections between the pipe guides; and the pipe spacer having a contracted condition, in which the interconnections are contracted and the pipe guides are moved into proximity to one another by movement of the travelling slips towards the stationary slips, and an expanded condition, in which the interconnections are extended and the pipe guides are moved apart from one another by movement of the travelling slips away from the stationary slips.
 9. An hydraulic snubber unit as claimed in claim 8, wherein the extendable and contractible interconnections comprise two parallel sets of tubular members, the tubular members of each of the sets being telescopically extendable and retractable relative to one another, and each including a connecting member for telescopically extending and contracting the tubular members, the connecting members each having one end connected for movement with the travelling slips and an opposite end extending into the tubular members.
 10. An hydraulic snubber unit as claimed in claim 8, wherein each of the connecting members has at one end thereof an anchor member located within an innermost one of the tubular members of the respective set of tubular members, said innermost tubular member having an end abutment engageable by the anchor member to telescopically extend said innermost tubular member.
 11. An hydraulic snubber unit as claimed in claim 10, wherein each of the tubular members of each set, other than an outermost one of the tubular members, has on one end thereof a further anchor member and each of the tubular members has at an opposite end thereof a further end abutment, the further end abutment being engageable by one of the further anchor members to effect the telescopic extension of the tubular members.
 12. An hydraulic snubber unit as claimed in claim 8, wherein the extendable and contractible interconnections comprise two parallel sets of telescopically extendable and retractable tubular member connecting the pipe guides in a ladder-like assembly.
 13. A method of guiding a pipe as the pipe is being snubbed through snubbing unit having stationary snubbing slips, traveling snubbing slips and hydraulic jacks for moving the traveling slips towards and away from the stationary slips, the hydraulic jacks comprising hydraulic cylinders and jack rods extending from the hydraulic cylinders, the jack rods being connected to the traveling snubbing slips, the method comprising the steps of:—gripping the pipe by the travelling snubbing slips during movement of the pipe through the snubbing unit; extending and retracting the hydraulic jacks to displace the travelling snubbing slips relative to the stationary snubbing slips and thereby to displace the pipe through the snubbing unit; and guiding a section of the pipe extending between the stationary snubbing slips and the travelling snubbing slips by laterally restraining the pipe section at intervals spaced apart along the section of the pipe.
 14. A method as claimed in claim 13, in which the step of guiding a section of the pipe comprises guiding the pipe by pipe guides spaced apart along the section of the pipe, and which further includes moving the pipe guides towards one another on movement of the travelling slips towards the stationary slips and moving the pipe guides apart from one another on movement of the travelling slips away from the stationary slips.
 15. A method as claimed in claim 14, which includes guiding the pipe guides along the pipe by sliding engagement of the pipe guides with the jack rods of the hydraulic cylinders. 